This study examines temporal spacing between successive broods of song sparrows on Mandarte Island, British Columbia, Canada. In 1977 and 1978 brood spacing was strongly influenced by the size of the earlier brood. In 1978 only, pairs with more nesting experience were able to renest sooner. Song sparrow females did not begin to incubate a later clutch while caring for more than one fledged young. Triple-brooded females took less time on average from fledging earlier broods to beginning subsequent ones and raised more young per season than females breeding twice.Although large broods delay renesting, a simple model shows that the extra time required to raise large broods does not influence the optimal brood size in Mandarte Island song sparrows. A similar model for the great tit (Parus major) suggests that season length may influence optimal brood size in this species.Clutch size in Mandarte Island song sparrows does not vary consistently within seasons or among years. Reproductive success was uniform for the first two-thirds of the breeding season, but late nests produced few independent young. Clutches of four eggs were most common and produced more young on average than did clutches of three.
